Gas filter mask on Mars - sci fi

[DaveC426913]

TL;DR Summary

In Kim Stanley Robinson's Mars Series, they had gas masks that preferentially let oxygen through. Can that work?

In the early parts of the books, Mars' ambient atmo pressure (and temperature) was increased, including not just CO2, but oxygen as well.

It rose to the point where they only needed masks that let through oxygen but not CO2.

In my amateur view, I would expect that this would not work very well. I see the partial pressure of oxygen entering the mask as being insufficient for breathing - they would be gasping for air and sucking deeply with every breath just to get oxygen.

Of course, it would be very dependent on the ambient atmo pressure and the concentration of oxygen...

Let's assume the masks are passive, not actively taking in oxygen and pressurizing it.(While this is couched in a sci-fi story, the physics is real - and could conceivably work today for high altitudes - so i figure this is a more appropriate forum than Sci-Fi.)

 

[BillTre]

In theory, you could filter at a molecular level of fineness and only pass molecules of some particular size. If oxygen is the smallest size molecule, that could work. However, the membrane would be like a membrane in a reverse osmosis machine or membranes used in dialysis. The resistance to flow/surface area would be large. RO machines often use pumps to push water through their membranes.

An alternative could be sending the air through soemthing like a resin that binds all the molecules you don't want. This would be a larger device, but with lower flow resistance. The filter material would get saturated however and would have to be replaced or treated to dump the bound molecules before it would be useful again.

 

[DaveC426913]

That's all good to know.

To me, it seems as simple as: with only a partial pressure of oxygen at the face mask, and full ambient pressure on the body (i.e. lungs), a person would have to struggle to inhale - like trying to use a hollow reed to breathe at the bottom of a pond.

 

[Rive]

Correct. Unless there's some kind of inert gas circulated within the breather to equalize the pressure like in some types of diving or similar breathing devices, the breathing capacity will be limited by the tolerance of muscles involved.

 

[DaveC426913]

Correct. Unless there's some kind of inert gas circulated within the breather to equalize the pressure like in some types of diving or similar breathing devices,

I am not sure I see how this would work.

the breathing capacity will be limited by the tolerance of muscles involved.

If you transpose this from abstract to practical, ie. by imagining what it would be like to use such a device, I think anyone would categorize it as non-viable except as an emergency device. No device that makes you feel like you're sucking vacuum would be tolerable for more than a few minutes.

 

[Rive]

am not sure I see how this would work

Think of it as a special type of rebreather where the oxygen supply comes by filtering the 'air'.

 

[jim mcnamara]

During cold periods on Mars the surface temperature would require a human to have 100% "coverage". So why try to create a mask in addition to whatever shield you have against the cold.

The predication for this thread is kind of weird, the topic of partial pressure enhancement itself is first rate. I'm not sure where the thread should be.

Do not neglect thermodynamics - it will require substantial energy to increase the partial pressure of anyone gas in the Martian atmosphere up to something compatible with Earth life. There is no free lunch on this one.
Low partial pressures of $O_2$ will suck oxygen out of the pulmonary system otherwise.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6420699/

 

[jim mcnamara]

PS: Very low $PCO_2$ levels also affect the pulmonary system, too. Our pulmonary system evolved on Earth for ±300 million years, so there are lots of gotchas going to other planets

 

[DaveC426913]

What about positioning the filter at the intake of an air compressor?

See OP:

Let's assume the masks are passive, not actively taking in oxygen and pressurizing it.

 

[notenoughscience]

See OP:

Well that's embarrassing. Thanks for pointing that out.